When electric signs were originally employed, the designs were cut into opaque material and lights were placed behind the opaque material to make the designs stand out. As new techniques became available, designs were formed by light bulbs and in some cases by neon tubes or the like.
In various electric signs, circuits are provided such that some lights are on while other lights are turned off and the sign illuminates first one design and then another. Some of the modern signs display movement and this is achieved by an automatic switching between light bulbs and other such sources of illumination.
One type of electric sign employs transilluminated elements employing translucent plastic or glass. Light sources inside of such signs make messages and designs on the translucent plastic or glass more clearly visable.
The most significant qualities of an electric sign are brightness and clarity. The sign is designed to be bright so that it can be effectively seen. The sign is preferrably made clear so that it can be easily read.
Bulbs must be spaced at appropriate distances so that their fields of light will not interfere with one another. A sign should be evenly lighted so that each letter and part of the associated design stands out and is clear.
Competition between signs has led to the use of brighter light and the use of electric signs for advertising has become so widespread that vast industries have been built on the same. Most signs are, however, extremely costly and this is especially so where some form of sequencing is provided for the various lights incorporated therein.